Skirts for surface effect devices to reduce drag and air cushion disturbances



P 1957 P. F. GUIENNE 3,339,55

SKIRTS FOR SURFACE EFFECT DEVICES TO REDUCE DRAG AND AIR CUSHION DISTURBANCES Filed Oct. 18, 1965 2 Sheets-Sheet l Imam pau/ [wanna/'5 'a/enne Sept. 5, 1967 P. F. GUIENNE SKIRTS FOR summon EFFECT DEVICES TO REDUCE DRAG Filed Oct. '18, 1965 AND AIR CUSHION DISTURBANCES 2 Sheets-Sheet 2 25 1/% 22,s ,zo

Inyenz/or pd u/ Franco/5 a 's/ma Fitorn eys United. States Patent SKIRTS FOR SURFACE EFFECT DEVICES T0 RE- DUCE DRAG AND AIR CUSHION DISTURB- ANCES Paul Francois Guienne, Paris, France, assignor to Bertin & Cie, Paris, France, a company of France Filed Oct. 18, 1965, Ser. No. 497,165 Claims priority, application France, May 26, 1%5,

4 Claims. (01. 1so-7 Land and water craft are known which are borne while in movement by air cushions produced by some appropriate form of air-compressing system, the cushions being intermediate the craft and the ground or water.

In order that the air supplying the cushions may be confined laterally, the use has been suggested of solid enclosures which open towards the ground or water and which receive the compressed air or gas. In this context the term air cushion shall be understood as covering fluid cushions of any kind.

One of the problems arising with enclosures of this kind is the need to reduce very considerably disturbances to the air cushion and drag caused by unevennesses in the surface of the ground or water above which the vehicle is required to be maintained and to move.

This invention relates to a particular enclosure construction helping to solve the problem.

According to a first feature of the invention, the enclosures in shape resemble truncated cones whose major base is closed and secured to the vehicle while the minor base opens towards the ground or water, the cone axes and the front and rear generatrices inclining downwards towards the vehicle rear, the word rear being understood in the light of the direction of vehicle movement. Clearly, inclining the generatrices in this way facilitates passage of the craft over unevennesses in the surface over which the craft is moving. More particularly in the case of water craft, inclining the rear generatrix facilitates the removal of heavy seas entering an enclosure, whereas were the rear generatrix to be inclined in the opposite direction, the rear part of the enclosure might form a scraper with a sheet of water sticking to it while the craft is in motion.

The enclosures can be made of some fairly rigid substance, such as metal, more particularly for a marine craft. Preferably, however, and more particularly for land craft, the enclosures are made of some air-impervious flexible substance, such as rubberised fabric.

In this case, the shape according to the invention as just defined makes it difficult to stabilise the enclosure in respect of continuous forcesi.e., the internal air pressure-and transient forcesi.e., reaction of obstacles. Stabilisation can, it is found, be achieved, if, in accordance with the invention, the ratio of enclosure height to enclosure major base, and the angle at the top of the geometric cone hearing it, and the angle of inclination of the cone axis, are chosen within limits to be specified hereinafter.

For a better understanding of the invention and to show how the same may be carried into effect, reference may now be made to the accompanying drawings wherein:

FIG. 1 is a perspective view of a flexible enclosure or skirt according to the invention;

FIG. 2 shows the same enclosure but sectioned along its plane of symmetry;

FIG. 3 is a graph showing the limits for the angles on and B of FIG. 2, and

FIG. 4 is a diagrammatic plan view of a craft having enclosures or skirts according to the invention.

The enclosure or skirt shown in FIGS. 1 and 2 have the shape of a truncated cone 1 having its major base secured to the underside of a frame 2 of a land vehicle or to the underside of a ships hull; the minor base 3 of the cone opens towards the surface 4 between which and the craft it is required to produce a lift cushion. In the particular example shown, the surface 4 is the surface of the ground.

Through a duct 5 from some form of air compressor (not shown), compressed air is supplied to the chamber bounded by the enclosure 1 and the vehicle platform or hull or the like 2. The pressure of the air in the enclosure 1 acts upwards on the frame or hull 2 and tends to lift the same off the ground, and the frame 2 rises as far as an equilibrium position in which the air leaking between the ground and the base 3 is such that the pressure in the enclosure 1 is enough to keep the frame 2 lifted clear of the ground. If a number of similar enclosures, as e e e e e (FIG. 4), are provided below a vehicle, the vehicle can be arranged not to rest directly on the ground but to be borne by air cushions, so that the vehicle can be propelled by a relatively small force. Of course, it is advisable for the enclosures to be supplied independently of one another so that a brief pressure drop in any single one enclosure does not react on all the others.

The enclosure shown in FIGS. 1 and 2 in shape resembles a cone having a skew axis AA forming an angle a with the vertical, orientation being such that the axis AA inclines downwards in the opposite direction to the direction F of vehicle traveli.e., so that the axis AA inclines down towards the vehicle rear. Also, the half-angle 3 at the cone apex is so adapted to the angle a that the rear generatrix GG also inclines downwards and to the rear. Clearly, the advantage of this feature is that it facilitates the removal of any foreign bodies entering the enclosure while the vehicle is in movemente.g., stones or earth in the case of a land vehicle, and water in the case of a marine vehicle.

Advantageously, the enclosure is made of a flexible airimpervious substance, such as a rubberised fabric, since the enclosure is then deformable and can adapt itself to unevennesses in the surface of the ground or water. The enclosure can readily be contrived with a conical shape if a strip or band of flexible material is cut appropriately, wound to the shape of the truncated cone, and secured along the joining generatrices. The enclosure can be secured to the vehicle by any appropriate means, for instance, by being clamped by a steel-wire ring 7 to a circular lip or the like 6.

I have found that the dimensions and angles must stay within some proportion limits to ensure stability of shape of the enclosure, for the same internal pressure of the cushion fluid and external actions such as are caused by unevennesses in the ground or waves of water. For satis factory shape stability, the following two conditions must be observed:

(1) If H is the height of an enclosure and D the diameter of its major base, then:

(2) If the values of the angle a are plotted as ordinates and the values of the apex angle 25 of the cone to which the enclosure is cut are plotted as abscissae, the result is the graph which is given in FIG. 3 and in which the lines bounding the polygon abcd enclose an area containing those values of the angles a and 2B which give a stable shape.

The co-ordinates in angle degrees (sexagesimal division) of the four points a, b, c, d, are as follows:

a b c d a 22.5 30.0 20 5 2 10 22.5 40 10' The equations for the four straight lines ab, bc, cd, and da bounding the stability area are therefore:

(ab) a22.5 2

(be) x30 2B-22.5

( a20 2B4O (1-5 2fi10 What I claim is:

Y 1. A pressure gas cushion sustained movable body comprising a platform with an underface, and a wall depending from said underface and adapted to enclose laterally said cushion, said wall being in the shape of a frusturn of a cone having a closed top larger base attached to said platform and an open bottom smaller base facing the surface over which said body is designed to move, the axis of said frustum of a cone as well as the rearmost generatrix thereof being inclined from top to bottom towards the rear of said body.

2. Movable body as claimed in claim 1, wherein said 7 wall is made of flexible material.

3. Movable body as claimed in claim 1, wherein the ratio between the height of said, frusto-conical wall and the diameter of said top larger base thereof is comprised between about 0.25 and 0.8.

4. Movable body as claimed in claim 1, wherein said frusto-conical Wall has its axis inclined at an angle on to the vertical and its vertex opening at an angle such that, on a graph in which on is plotted against 2 8, the respective values of a and Zfl are included in a quadrilateral whose vertices have substantially the following coordinates: (oz=22.5, 25:10"), (01:30, 25:22.5), (a=20,2fi=40) and (oc=5, 26:10").

References Cited UNITED STATES PATENTS 3,254,731 6/19 66 Schreiber -7 FOREIGN PATENTS Ad. 80,047 1/ 1963 France.

A. HARRY LEVY, Primary Examiner. 

1. A PRESSURE GAS CUSHION SUSTAINED MOVABLE BODY COMPRISING A PLATFORM WITH AN UNDERFACE, AND A WALL DEPENDING FROM SAID UNDERFACE AND ADAPTED TO ENCLOSE LATERALLY SAID CUSHION, SAID WALL BEING IN THE SHAPE OF A FRUSTUM OF A CONE HAVING A CLOSED TOP LARGER BASE ATTACHED TO SAID PLATFORM AND AN OPEN BOTTOM SMALLER BASE FACING THE SURFACE OVER WHICH SAID BODY IS DESIGNED TO MOVE, THE AXIS OF SAID FRUSTUM OF A CONE AS WELL AS THE REARMOST GENERATRIX THEREOF BEING INCLINED FROM TOP TO BOTTOM TOWARDS THE REAR OF SAID BODY. 